Technology of milling bridge plugs and field applications in shale gas horizontal wells with severe casing deformation

Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings, increasing the risk of stuck drill bits. Friction in the wellbore further complicates tool deployment into the horizontal section, posing challenges to efficient plug drilling and achieving wellbore access to the target layer. This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells. It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements, including the timing of plug drilling, extending the run in the horizontal section, parameter control, and real-time field analysis. Field practices have shown that after casing deformation occurs, priority should be given to drilling out the bridge plugs below the point of deformation. The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes. Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks. If sticking occurs, high-tonnage pulling should be avoided. Instead, releasing the stick through up-and-down string motion, combined with high-volume nozzle spraying and annulus pumping, is recommended. The selection of coiled tubing should consider diameter, wall thickness, and steel grade to handle complex situations. Larger diameters, thicker walls, and low-frequency, multi-head hydraulic oscillators are more effective for unlocking horizontal sections. This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups, offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.